Abstract. As a part of the IPY project POLARCAT (Polar Study using Aircraft, Remote
Sensing, Surface Measurements and Models, of Climate Chemistry, Aerosols and
Transport), this paper studies the sources of equivalent black carbon (EBC),
sulphate, light-scattering aerosols and ozone measured at the Arctic
stations Zeppelin, Alert, Barrow and Summit during the years 2000–2007.
These species are important pollutants and climate forcing agents, and
sulphate and EBC are main components of Arctic haze. To determine where
these substances originate, the measurement data were combined with
calculations using FLEXPART, a Lagrangian particle dispersion model. The
climatology of atmospheric transport from surrounding regions on a
twenty-day time scale modelled by FLEXPART shows that the stations Zeppelin,
Alert and Barrow are highly sensitive to surface emissions in the Arctic and
to emissions in high-latitude Eurasia in winter. Emission sensitivities over
southern Asia and southern North America are small throughout the year. The
high-altitude station Summit is an order of magnitude less sensitive to
surface emissions in the Arctic whereas emissions in the southern parts of
the Northern Hemisphere continents are more influential relative to the
other stations. Our results show that for EBC and sulphate measured at
Zeppelin, Alert and Barrow, northern Eurasia is the dominant source region.
For sulphate, Eastern Europe and the metal smelting industry in Norilsk are
particularly important. For EBC, boreal forest fires also contribute in
summer. No evidence for any substantial contribution to EBC from sources in
southern Asia is found. European air masses are associated with low ozone
concentrations in winter due to titration by nitric oxides, but are
associated with high ozone concentrations in summer due to photochemical
ozone formation. There is also a strong influence of ozone depletion events
in the Arctic boundary layer on measured ozone concentrations in spring and
summer. These results will be useful for developing emission reduction
strategies for the Arctic.